Oc78 Unit 10: Environmental Change The MOST Important Problem! The study of the evidence Evidence is a piece of information that supports a conclusion. Most of what people believe is unsupported by evidence. Nevertheless, ideas are stronger when backed by information that your audience accepts. It is important to distinguish scientific from nonscientific forms of evidence. It is important to distinguish evidence from nonevidence. Dating Techniques Radioactive decay o The idea of life. Carbon 14: 5730 yr. life present in all living organisms Cosmic ray proton hits nucleus of atom releasing a highspeed neutron which strikes a nitrogen atom, changing it into radioactive carbon 14. Can further combine with oxygen to form CO2, which combines with plants (who dont Assumption: same amount of C14 in atmosphere today as in the past. o There is a limit to the number of halflives (cant date very old or young specimens) Oxygen isotopes can be used as an indicator of temperature. Evaporation : O16 enriches vapour, moves onto land and runs off to ocean during warm period, but during glacial periods is deposited in ice on the land and remains there. O18 in the water is higher at these times. These ratios can be used to determine temperature. Stratigraphy Law of superposition: sedimentary layers are deposited in a time sequence, with the oldest on the bottom and the youngest at the top. Using Pollen Pollen grains are very distinctive and different from one another. Pollen grains and spores can be used for paleoclimate reconstruction , this study is known as pollen analysis, or palynology.